Tissues require the presence of resident macrophages for their normal development and function and macrophage adhesion and motility are critical components of this tissue/macrophage functional interaction. Macrophages may also play an important role, via their motility and invasiveness, in promoting the progression of solid tumors to an invasive metastatic phenotype. Colony Stimulating Factor-1 (CSF-1) is the primary growth factor regulating macrophage survival, proliferation, differentiation, and morphology in different tissues. Protein tyrosine phosphatase ? (PTP?) mediates the morphological effects of CSF-1 in macrophages by dephosphorylating paxillin, leading to paxillin depletion from focal complexes, decreased adhesion and increased motility. Paxillin is an adaptor molecule that is tyrosine phosphorylated in response to growth factor stimulation and cell adhesion and is important in focal complex formation. Tyrosine residue-specific phosphorylation/dephosphorylation is likely to be important in co-ordination of downstream signaling from paxillin. The interaction between PTP? and paxillin appears to be stabilized by the adaptor function of the tyrosine kinase, Pyk2. PTP? expression is decreased in germinal center B cells that are temporarily immobilized, suggesting a similar role for PTP? in B cell adhesion and motility as in macrophages. Preliminary evidence indicates that BCL-6, a transcriptional repressor that regulates lymphoid development and germinal center formation, may repress PTP? expression. Further, genetic activation of BCL-6 underlies ~30% of diffuse large cell B cell lymphomas and PTP? expression is decreased in these tumors. Preliminary evidence also suggests that, apart from regulating PTP? mRNA expression, CSF-1 rapidly regulates PTP? activity post-translationally. Based on these observations, we propose that: 1) PTP? is regulated both transcriptionally and post- translationally by CSF-1, 2) PTP? targets one or more specific phosphotyrosine residues on paxillin for dephosphorylation, using Pyk2 as an adaptor, and 3) by regulating macrophage adhesion and motility, PTP? is important in mouse development and macrophage function. The overall aim is to further delineate the mechanisms by which PTP? exerts regulatory control of macrophage adhesion and motility. The specific aims are: 1. To investigate the regulation of macrophage PTP? expression and activity in response to CSF-1. 2. To elucidate the role of PTP? in the regulation of paxillin tyrosine phosphorylation. 3. To determine the role of PTP? in mouse development and macrophage function.